Air compressor



United States Patent 2,723,798 AIR COMPRESSOR Donald F. Straitilf, Greensburg, Pa., assignor to Wes tinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Application February 24, 1954, Serial No. 412,262 Claims. (Cl. 230-208) This invention relates to air compressors and more particularly to means for controlling the operating temperatures thereof.

In a copending George L. Cotter application, Serial No. 363,202, filed June 22, 1953, and assigned to the assignee of the present application, there is disclosed a fluid pressure responsive apparatus for effecting admittance of 1 dependently of the compressive action of the piston movement and consequently without the corresponding generation of heat, thereby reducing the amount of work performed by said piston in raising the pressure in the cylinder from atmospheric pressure to discharge pressure and thus reducing the heat of compression generated per stroke below that which would prevail without admission of the cooled compressed air. 7 7

It is the prime object of the present invention to provide an improved and simplified fluid pressure control apparatus for controlling such admittance of the cooled compressed air into the compressor cylinder duringeach compression stroke of the compressor piston to serve the same purpose as set forth above.

Other objects and advantages will become apparent from the following more detailed description of the invention taken in connection with the accompanying drawing in which the single figure is an elevation view, partly in outline and partly in section, of a fluid pressure controlled, cooling air admittance controlled apparatus embodying the invention and shown in association with a piston type air compressor. 7 Description Referring to the drawings, the air compressing system with the cooling air admittance control apparatus is associated comprises an air compressor 1, a storage reservoir 2, after cooler coils 3.

For the purpose of illustration,'the air compressor 1 comprises a cylinder casing 4 having the usual piston 5 reciprocable therein in slidable sealing engagement with the usual inner cylinder wall 6 formed'in said casing. 24 in the casing 21 as Shown in the drawing?! In the well-known manner, the piston 5 serves as a movable abutment defining one end of the usual cylinder chamber 7, the opposite end of which chamber 7 is closed by a pressure head 8, with which is associated the usual inlet and discharge valves 9 and 10, respectively, which control admission offree air to and discharge of compressed air from thecylinder chamber 7, respectively; inlet valve 9 being arranged to control communication between the atmosphere and the cylinder chamber 7. by

way of an inlet port 11; and the exhaust valve 10 being disposed in a discharge chamber 12 and arranged to control communication between the cylinder chamber 7 and the discharge chamber 12 by way of a discharge port 13. A light compression spring 14 is arranged to cooperate with the inlet valve 9 to urge same toward its seated position in which it is shown in the drawing closing off the cylinder. chamber 7 from the atmosphere. A similar compression spring 15, disposedin the discharge chamber 12, is arranged to'bias the discharge valve 10 toward its seated position, in which it is shown in the drawing, closing off the cylinder chamber 7 from the discharge chamber 12.

The piston 5 is arranged to be reciprocated through the medium of the usual crankshaft 16 and connecting rod 17.

In the well-known manner, movement of the piston 5 through its suction stroke from top dead center position in proximity of the pressure head 8 to bottom dead center position near which it is shown in the drawing will cause expansion of cylinder chamber 7 for admission of air from the atmosphere into said chamber 7 by way of inlet valve 9 and inlet port 11. Subsequent movement of the piston 5 through its compression stroke in the opposite direction, that is, from its bottom dead'center position to its top dead center position, will cause contraction of chamber 7 and resultant compression of the air in chamber 7 and displacement of such air therefrom by way of the port 13, discharge chamber 12, and the discharge valve 10.

Discharge chamber 12 is constantly connected to the reservoir 2 by way of the aftercooler coils 3 which remove latent heat of compression by cooling the compressed air discharged from the compressor enroute to the reservoir.

According to the invention, the fluid pressure control means for effecting admittance of cooled compressed air from the reservoir to the cylinder chamber 7 during each compression stroke of the piston 5, for cooling purposes, comprises a port 18 in the wall of the cylinder casing 4 opening through the cylinder wall 6 in the compressor 1, and a fluid pressure responsive device 19.

The port 18 in the cylinder casing 4 is so disposed as to be covered by the compressor piston 5 when same is in proximity of its top dead center position, for example, during eighty degrees of crankshaft rotation as piston 5 completes its compression stroke and begins its suction stroke relative to its top dead center position. During the remaining portions of the suction and compression strokes the port 18 will be uncovered and open to the cylinder chamber 7 in the compressor 1, for reasons which hereinafter will become apparent.

The fluid pressure responsive device 19 for controlling, in conjunction with the port 18, admittance of cooling air to the cylinder chamber 7 in the compressor 1 comprises a flexible diaphragm 20, preferably of metal, clamped at its outer peripheral edge between divided portions of a casing 21 and subject opposingly to pressure of gas in chambers 22 and 23 at its opposite sides, respectively, formed within the casing 21. Diaphragm 20 is preferably disc-shaped and correspondingly the chambers 22 and 23 are preferably cylindrical in form. The chamber 23 is adapted to be connected to the port 18 in the compressor 1 through the medium of a port pipe or nipple 25; it being desirable, however, that such connection be made as short as possible to reduce the additional volume to which the cylinder chamber 7 will be connected during the suction stroke of the piston and for this reason it is preferable that the casing 21 be mounted directly on a cylinder casing 4 for registry of ports 18 and 24 to eliminate the necessity for any extension such as the pipe or nipple 25. The pipe or nipple 25 is shown for sake of simplicity in the schematic representation employed in the drawing.

The chamber 23 is also adapted to be connected to the reservoir 2 to become availed of cooled compressed air stored therein through the medium of a central port 26, opening through the respective portion of the casing 21, and a pipe 27. A resilient annular seat 28 is disposed in the chamber 23 in encirclement of the port 26 and suitably attached or bonded to the respcctiveportion of the casing 21 for cooperation with the diaphragm 20 to control communication between'lthe chamber-23 and the pipe 27. A compression spring 29 disposed in portion of the casing 21; a suitable groove or recess being formed in said portion to accommodate location of the spring. In addition, the diaphragm 20 is provided with an equalizing port or ports 30 which preferably are disposed symmetrically about the diaphragm 20 in encirclement of the annular seat 28.

Operation In operation of the improved fluid pressure apparatus or system for controlling admittance of cooling. air to a reciprocating type air compressor, assume that the reservoir 2 is charged with compressed air from which the heat of compression has been removed by such as the aftercooler coils 3 enroute from the compressor device 1. Assume, also, that the compressor 1 is in operation and that the piston 5 therein has just completed its suction stroke for causing admittance of initial charge of atmospheric air into the cylinder chamber 7 which is therefore filled therewith, and that said piston 5 is beginning its compression stroke and in such position in which it is shown in the drawing. When, as a result of movement of the piston 5 during its compression stroke, the pressure of air in the cylinder chamber '7 attains a pressure of such as twenty pounds for example, corresponding to a crankshaft rotation of such asapproximately seventy degrees after bottom dead center position of the piston, such pressure as experienced in the pressure chamber 23 in the pressure responsive device 19 via the compressor cylinder port 18 will cause the diaphragm 20 to deflect in the direction of chamber 22, thereby unseating said diaphragm from the resilient annular seat 28 to allow cooled compressed air from the reservoir 2 to flow by way of the pipe 27 and port 26 in the casing 21 of device 19 into the chamber 23, thence to the cylinder chamber 7 in the compressor 1 by way of the port 24, the pipe or nipple 25, and port 18 in said compressor. Such cooled compressed air is thus admitted into the cylinder chamber 7 for mixture with the initial charge of atmospheric air therein to raise the pressure of the charge in said chamber independently of the compressive action of the piston 5 and consequently without the generation of corresponding heat of compression, thereby to provide for cooler operation of the compressor cylinder 1 than would otherwise prevail without provision for cooling of said compressor.

At the same time that cooled compressed air from the reservoir 2 is traveling through the pressure chamber 23 in the device 19 to the compressor cylinder chamber 7, such compressed air in the chamber 23 will flow also to the pressure chamber 22 at the opposite side of the diaphragm 20 through the equalizing ports 30. At such time, however, by virtue of the restrictive action of the equalizing ports 30, a preponderance in pressure in the chamber 23 over that pressure in the chamber 22 will be maintained sufficient to hold the diaphragm 20 unseated and disposed away from the annular seat 28 against the opposition of the control spring 29.

When, during each successive compression stroke of the compressor piston 5, said piston in approaching its top dead center position closes off the cylinder port 18, the fiow of compressed air from the reservoir 2 by way of the device 19 to the compressor cylinder chamber 7 will terminate and final movement of the piston to its top dead center position will cause the compressed air in the cylinder chamber 7 to be expelled therefrom to the reservoir 2 by way of the aftercooler coils 3. The compressor piston then begins its suction stroke from top dead center position in the direction of its bottom dead center position while the port 18 remains covered by the piston 5.

During the time that the port 18 in the cylinder casing 4 is covered by the piston 5, the fluid under pressure from the chamber 23 on one side of the diaphragm 20 will continue to flow to the chamber 22 at the opposite side of said diaphragm by way of the ports 30, and such flow will be in behalf of equalization of the pressures of the two chambers 22 and 23 to the extent that the spring 29 will return the diaphragm 20 to its seated position, in which it is shown in the drawing, in engagement with the annular seat 28 encircling port 26 to again close otf the chamber 23 from the reservoir 2 before the piston 5, moving through its suction stroke, again uncovers the cylinder port 18.

Subsequently, when the piston 5 moving through its suction stroke uncovers the port 18 initially, the compressed air present in the chambers 22 and 23 in the device 19 at that time will exhaust to the cylinder chamber 7 by way of the port 24 in said device 19, the pipe or nipple 25, and the port 18; that compressed air in the chamber 22 exhausting by way of the ports 30 in the diaphragm 20 and said chamber 23.

At the end of the suction stroke of the piston 5 and at the beginning of its compression stroke, pressure of the air in the chamber 7 and therefore in the chamber 23 in device 19 connected thereto by way of port 18 will be of substantially atmospheric pressure, while the pressure of air in the chamber 22 in device 19 at the opposite side of the diaphragm 20 will be in excess of that in chamber 23 by virtue of the restrictive action of the ports 30 in said diaphragm through which compressed air in chamber 22 was released to cylinder chamber 7 during the suction stroke of the piston 5.

During the beginning of each successive compression stroke of the piston 5 the pressure of the initial charge of the air in the cylinder chamber 7 and therefore in the pressure chamber 23 in the device 19 will again cause diaphragm 20 in device 19 to be unseated against opposition of spring 29 and the pressure existent in the chamber 22 at that time to again call for admission of the cooled compressed air from the reservoir 2 to the cylinder chamber 7 as aforedescribed. It will thus be appreciated that the device 19, in cooperation with the port 18 in the cylinder device 1, will function to automatically effect supply of cool compressed air to the cylinder chamber 7 during each compression stroke of the compressor piston 5 for purposes of cooling. From the foregoing it will be appreciated that if the pressure of fluid in the reservoir 2 is considerably above that pressure of fluid in the cylinder chamber 7 and in chamber 23 in device 19 immediately prior to closure of the port 18, the chamber 23 will experience an increase in pressure immediately upon closure of the port 1.8 which will increase the burden placed upon the ports 30 in the diaphragm 20 to effect equalizing of the pressures in chambers 22 and 23 during the interval that said port 18 remains closed. For this reason, it may be desirable to provide a regulating valve 31 in the pipe 27 interposed in the pipe 27 between the device 19 and the reservoir 2 for automatically regulating and limiting the pressure of the cooling air admitted to the device 19 and thereby to the compressor 1 to a value in only slight excess of that existent in the cylinder chamber 7 at time of closure of the cooling air supply port 18.

From the foregoing it will be apparent that during the time that the reservoir pressure is first being builtup to its normal operating pressure by compressor operation, the pressure in the compressor cylinder chamber 7 created by movement of the piston 5 during the compression stroke may be sufiicient to unseat diaphragm 20 in device 19 and suflicient to discharge into the reservoir 2 via port 26 in said device 19 in by-pass of discharge valve 10 and coils 3 before said piston covers the port 18. While the system might operate in such fashion satisfactorily during such initial build-up in reservoir pressure, it may be desirable to effect a cooling of the compressed air delivered to the reservoir 2 even during such initial build-up, in which case a check valve 32 may be provided in the pipe 27 to prevent such cooling coil by-pass flow to the reservoir.

Summary Thus it will be seen that I have provided a relatively simple and an inexpensive means for automatically controlling admittance of cooling air to a compressor cylinder during each of its successive compression strokes to provide for cooler operation of said compressor.

Having now described the invention, what I claim as new and desire to secure by Letters Patent, is:

1. In combination with a source of cooled compressed gas and a reciprocating piston type compressor having a cylinder chamber and operable to cause admission of an initial charge of gas to be compressed into said cylinder chamber and compression of said initial charge within said cylinder chamber and its consequent discharge therefrom, a fluid pressure responsive device having a supply port in fluid pressure communication with said source of cooled compressed gas and comprising a valve seat encircling said supply port, said device also having one fluid pressure chamber and a second fluid pressure chamber open restrictedly to said one fluid pressure chamber, flexible diaphragm valve means subject opposingly to pressures of gas in the two restrictedly interconnected chambers and cooperable with said valve seat to control communication between said supply port and said one fluid pressure chamber, said diaphragm valve means being biased into seating engagement with said valve seat to close said one fluid pressure chamber to said supply port, conduit means constantly open to said one fluid pressure chamber and adapted to be open to said cylinder chamber, and automatic means for establishing and disestablishing communication of said conduit means with said cylinder chamber according to the stroke of said piston type compressor to admit gas under pressure from said cylinder chamber to said one fluid pressure chamber for unseating said diaphragm valve means during a first stage of each compression stroke of said compressor, to permit gas under pressure from said source to flow via the unseated diaphragm valve means and said one fluid pressure chamber to said cylinder chamber during a subsequent stage of each successive compression stroke of said compressor, to close said one chamber to said cylinder chamber during the final stage of each successive compression stroke and the initial stage of each successive suction stroke of said compressor for terminating admittance of cooled compressed gas into said cylinder and permitting equalization of pressure of gas in said second fluid pressure chamber with that in said first fluid pressure chamber for reseating of said diaphragm valve means, and to open said one fluid pressure chamber to said cylinder chamber during the remainder of each successive suction stroke of said compressor for permitting release of fluid under pressure from said one fluid pressure chamber and thereby from said second fluid pressure chamber into said cylinder chamber to enable said diaphragm valve means to again be unseated by admittance of gas under pressure from said cylinder chamber during the following compression stroke of said compressor.

2. The combination as set forth in claim 1, further characterized in that said source of gas under pressure is charged with gas under pressure discharged from said compressor.

3. The combination as set forth in claim 1, including pressure regulating means in said supply conduit to limit the pressure of gas admitted to said one fluid pressure chamber from said source of gas under pressure when said diaphragm valve is unseated.

4. The combination as set forth in claim 1, including one-way flow valve means in said supply conduit to permit flow of gas under pressure from said source to said one fluid pressure chamber when said diaphragm valve is unseated and to prevent flow of gas under pressure from said gas compressing chamber to said source of gas under pressure when said diaphragm valve is unseated and the pressure of gas in said source is below normal.

5. In combination, a compressor casing having an inner cylinder wall defining the peripheral wall of a gas compressing chamber, a piston movable in axially slidable sealing engagement with said cylinder wall for movement alternately through a suction stroke to cause expansion of said gas compressing chamber for admittance thereinto of gas to be compressed and through a compression stroke to cause contraction of said gas compressing chamber for compression and discharge of the gas therein admitted during said suction stroke, said compressor casing also having a cylinder port opening therethrough into said cylinder wall in the path of travel of said piston for communication with said gas compress ing chamber, a source of gas under pressure from which heat of compression has been removed, and a fluid pressure responsive valve device comprising a hollow casing, a flexible diaphragm valve disposed in said hollow casing and dividing the interior thereof into one fluid pressure chamber at one side of said diaphragm valve and a second fluid pressure chamber at the opposite side of said diaphragm valve, a supply port in said casing opening said one fluid pressure chamber to the exterior of said casing, supply conduit means connecting said supply port to said source of gas under pressure for flow of fluid under pressure therefrom to said one fluid pressure chamber, a valve seat attached to and disposed Within said casing in encirclement of said supply port for engagement by said diaphragm valve to close said one fluid pressure chamber to said source of gas under pressure, bias means cooperative with said casing to constantly bias said diaphragm valve toward said valve seat, control and delivery port means in said casing opening said one fluid pressure chamber to the exterior of said casing, control and delivery conduit means connecting said control and delivery port means to said cylinder port for conveying gas under pressure from said gas compressing chamber to said one fluid pressure chamber during each successive compression stroke of said piston for unseating said diaphragm valve from said valve seat against opposition of said bias means and for conveying gas under pressure from said one fluid pressure chamber to said gas compressing chamber via said cylinder port once said diaphragm piston has thus been unseated during such compression stroke, and restricted communication means connecting said one fluid pressure chamber with said second fluid pressure chamber to permit flow of gas under pressure from said one fluid pressure chamber to said second fluid pressure chamber for enabling said bias means to reseat said diaphragm valve while said cylinder port is closed by said piston during the subsequent final stage of said pistons compression stroke and the initial stage of its following suction stroke, said restricted communication also providing for flow of gas under pressure from said second fluid pressure chamber to said gas compressing chamber via said one fluid pressure chamber and said cylinder port during the subsequent stage of said suction stroke to reduce the pressure of fluid in said second fluid pressure chamber sufliciently to permit the diaphragm valve to be again unseated during the following compression stroke of said piston.

References Cited in the file of this patent UNITED STATES PATENTS 2,389,720 Drane Nov. 27, 1945 FOREIGN PATENTS 46,384 France June 2, 1936 (Addition to No. 779,803) 

